Stimuli associated with behavioral events may induce physiological responses which serve adaptive functions for both the individual and the species. One of the primary models for study of these behavior/endocrine interrelationships has been the study of the mechanisms whereby reproductive behavior induces the neural and endocrine changes necessary for initiation and maintenance of pregnancy or pseudopregnancy (PSP) in the female rat. In this species, genitosensory stimulation received during mating initiates twice-daily surges of prolactin (PRL) which prolong ovarian corpora luteal activity necessary for gestation. The behavioral patterns exhibited by the estrous rat during mating are the lordosis posture, solicitational behavior patterns which serve to indicate sexual readiness, as well as the patterning, or pacing, of contact with males which regulates the sequence and timing of copulatory stimulation received. Pacing behavior has been observed under naturalistic conditions and is exhibited spontaneously by estrous females in the laboratory when they are placed into experimental test chambers which allow them to control their contacts with sexually active male rats. This intermittent display of approach toward and withdrawal from contact with males relies exclusively for its expression on the ability of the female to discriminate between the intensity of the copulatory mounts received throughout the mating sequence; females display selective responses to mounts - without intromission, intromission, and ejaculation. The resulting pattern of cervical-vaginal stimulation received significantly increases the incidence of PSP or pregnancy above levels seen in females mated under test conditions in which they are not able to pace coital stimulation. Furthermore, paced mating stimulates rapid increases in plasma concentrations of LH and the 5alpha-reduced androgen, 3alphaandrostanediol, and contributes to the mating-induced release of PRL which occurs within 1 hr after mating. Thus, genitosensory stimulation received by the female during paced mating initiates several neuroendocrine responses which may directly contribute to induction of PSP. Despite the compelling evidence that paced mating has significant consequences for reproductive success in the rat, very little is known about the mechanisms whereby genitosensory stimulation is transduced into neuroendocrine responses. Experiments proposed in this application will examine the particular genitosensory stimuli received during paced mating which are important for initiation of PSP/pregnancy. They will examine which brain areas receive neural input around the time of mating and determine whether these areas are important for induction of PSP. In addition, studies will examine the effects of 3alpha-androstanediol on the display of pacing behavior. Finally, experiments will examine whether paced mating influences post-mating transport of sperm within the female's reproductive tract and the numbers of offspring produced.